Antiangiogenesis or proangiogenesis for cancer therapy - PDF document

Anti-angiogenesis or pro-angiogenesis for cancer therapy 8376 Int J Clin Exp Med 2015;8(6):8369-8376 [25] Dickson PV, Hamner JB, Sims TL, Fraga CH, Ng CY, Rajasekeran S, Hagedorn NL, McCarville MB, Stewart CF and Davidoff AM. Bevacizumab- induced transient remodeling of the vascula - ture in neuroblastoma xenografts results in improved delivery and ef�cacy of systemically administered chemotherapy. Clin Cancer Res 2007; 13: 3942-3950. [26] Pastuskovas CV, Mundo EE, Williams SP, Nayak TK, Ho J, Ulufatu S, Clark S, Ross S, Cheng E, Parsons-Reponte K, Cain G, Van Hoy M, Majidy N, Bheddah S, dela Cruz Chuh J, Kozak KR, Lewin-Koh N, Nauka P, Bumbaca D, Sliwkowski M, Tibbitts J, Theil FP, Fielder PJ, Khawli LA and Boswell CA. Effects of anti-VEGF on pharmaco - kinetics, biodistribution, and tumor penetra - tion of trastuzumab in a preclinical breast can - cer model. Mol Cancer Ther 2012; 11: 752- 762. [27] Cesca M, Frapolli R, Berndt A, Scarlato V, Richter P, Kosmehl H, D’Incalci M, Ryan AJ and Giavazzi R. The effects of vandetanib on pacli - taxel tumor distribution and antitumor activity in a xenograft model of human ovarian carci - noma. Neoplasia 2009; 11: 1155-1164. [28] Bello E, Taraboletti G, Colella G, Zucchetti M, Forestieri D, Licandro SA, Berndt A, Richter P, D’Incalci M, Cavalletti E, Giavazzi R, Camboni G and Damia G. The tyrosine kinase inhibitor E-3810 combined with paclitaxel inhibits the growth of advanced-stage triple-negative breast cancer xenografts. Mol Cancer Ther 2013; 12: 131-140. [29] Chauhan VP, Stylianopoulos T, Martin JD, Popovic Z, Chen O, Kamoun WS, Bawendi MG, Fukumura D and Jain RK. Normalization of tu - mour blood vessels improves the delivery of nanomedicines in a size-dependent manner. Nat Nanotechnol 2012; 7: 383-388. [30] Carmeliet P and Jain RK. Principles and mech - anisms of vessel normalization for cancer and other angiogenic diseases. Nat Rev Drug Discov 2011; 10: 417-427. [31] Huang Y, Yuan J, Righi E, Kamoun WS, Ancukiewicz M, Nezivar J, Santosuosso M, Martin JD, Martin MR, Vianello F, Leblanc P, Munn LL, Huang P, Duda DG, Fukumura D, Jain RK and Poznansky MC. Vascular normalizing doses of antiangiogenic treatment reprogram the immunosuppressive tumor microenviron - ment and enhance immunotherapy. Proc Natl Acad Sci U S A 2012; 109: 17561-17566. [32] Webb T. Vascular normalization: study exam - ines how antiangiogenesis therapies work. J Natl Cancer Inst 2005; 97: 336-337. [33] Wong PP, Demircioglu F, Ghazaly E, Alrawashdeh W, Stratford MR, Scudamore CL, Cereser B, Crnogorac-Jurcevic T, McDonald S, Elia G, Hagemann T, Kocher HM and Hodivala- Dilke KM. Dual-action combination therapy en - hances angiogenesis while reducing tumor growth and spread. Cancer Cell 2015; 27: 123- 137. [34] Varki A. Trousseau’s syndrome: multiple de�ni - tions and multiple mechanisms. Blood 2007; 110: 1723-1729. [35] Caine GJ, Stonelake PS, Lip GY and Kehoe ST. The hypercoagulable state of malignancy: pathogenesis and current debate. Neoplasia 2002; 4: 465-473. [36] Levine M and Hirsh J. The diagnosis and treat - ment of thrombosis in the cancer patient. Semin Oncol 1990; 17: 160-171. [37] Mousa SA. Low-molecular-weight heparin in thrombosis and cancer. Semin Thromb Hemost 2004; 30 Suppl 1: 25-30. [38] Cool RM, Herrington JD and Wong L. Recurrent peripheral arterial thrombosis induced by cis - platin and etoposide. Pharmacotherapy 2002; 22: 1200-1204. [39] Molloy RG, Welch GC, Drury JK and Abel BJ. Arterial thrombosis after chemotherapy with cisplatin, vinblastine and methotrexate. Br J Clin Pract 1995; 49: 50-51. [40] Mousa SA. Anti-thrombotics in thrombosis and cancer. Future Oncol 2005; 1: 395-403. [41] Jain RK. Understanding barriers to drug deliv - ery: high resolution in vivo imaging is key. Clin Cancer Res 1999; 5: 1605-1606. [42] McDonald DM and Baluk P. Signi�cance of blood vessel leakiness in cancer. Cancer Res 2002; 62: 5381-5385. [43] Chia WK, Ali R and Toh HC. Aspirin as adjuvant therapy for colorectal cancer--reinterpreting paradigms. Nat Rev Clin Oncol 2012; 9: 561- 570. [44] Liao X, Lochhead P, Nishihara R, Morikawa T, Kuchiba A, Yamauchi M, Imamura Y, Qian ZR, Baba Y, Shima K, Sun R, Nosho K, Meyerhardt JA, Giovannucci E, Fuchs CS, Chan AT and Ogino S. Aspirin use, tumor PIK3CA mutation, and colorectal-cancer survival. N Engl J Med 2012; 367: 1596-1606. Anti-angiogenesis or pro-angiogenesis for cancer therapy 8370 Int J Clin Exp Med 2015;8(6):8369-8376 lature can also lead to a resistance of tumor cells to radiation therapy and many chemother - apeutics. In addition, hypoxia upregulates the production of angiogenic factors by cancer and stromal cells, which further aggravate vessel disorganization and thereby fuel non-produc - tive angiogenesis

in an endless self-reinforcing loop. For more than a decade, one of the approaches in cancer treatment has been targeting angiogenesis-the development of new blood vessels from pre-existing ones in the tumor microenvironment. Signi�cant efforts have focused on anti-angiogenic strategies aimed at reducing tumor blood vessel density to inhibit tumor growth [5]. Unfortunately, anti-angiogen - ic strategies have not been very successful in the clinic and multiple factors have been found to contribute to increased tumor aggressive - ness and therapy resistance following this kind of treatment. Anti-angiogenic agents can increase tumor hypoxia, promoting the selection of more-aggressive cancer cells that can proliferate under oxygen-de�cient condi - tions, and reduce chemotherapy delivery, for instance. However, increasing evidence [6, 7] suggests that vascular endothelial growth factor (VEGF) inhibitors can restore a balance between pro- and anti-angiogenic cytokines, tumor vessels, at least transiently, display a structural and functional phenotype more re�ective of normal blood vessels [8]. This process, termed vascu - lar normalization, remodels tumor vessels and partially overcomes the physiological barriers to drug and oxygen delivery within tumors through improvement in their functional ef�ciency, thus enhancing the delivery and anti - tumor activity of chemotherapy and radiation. However, this process of vascular normaliza - tion seems to be transient with a relatively narrow window during which synergy is likely to be achieved, and after which, the tumor vascu - lature is destroyed. Vascular normalization is a strategy to enhance the antitumor effects of chemotherapeutics, but this is time and dose dependent and therefore dif�cult to implement clinically. Thus, alternative strategies that over - come these issues are needed. Accumulating scienti�c dada demonstrate an alternative approach called “vascular promotion therapy” can increase chemotherapy delivery and intra - cellular uptake of the drug and reduces hypoxia by increasing tumor blood vessel density, blood �ow, leakiness, and dilation, which leads to reduced cancer growth and metastasis. In this article, we �rst summarize the structural and functional abnormalities of the tumor microvasculature to highlight the importance of this phenomenon for chemotherapeutics distri - bution. Next, we summarize the limitations of anti-angiogenesis in cancer treatment, discuss some key prototypical underlying mechanisms of vascular normalization and initial clinical evidence of vascular promotion therapy, and speculate on the clinical potential of anticoagu - lation as a novel paradigm to improve cancer treatment. Abnormality of tumor vasculature Classic laws that explain hemodynamic and transcapillary �ow can only in part explain the permeation of drugs into tumor tissue. Fick’s law, which states that the diffusion rate of small molecules depends on their concentration gra - dient, and Starling’s forces, which describe the capillary �ltration movement of �uids and mac - romolecules [9, 10] are useful mathematical means to de�ne the extravasation of drugs and their distribution in tissue but are not exhaus - tive for a situation as complex as that of tumors. Tumor vessels are tortuous; they follow a serpentine course, branch irregularly in a chaotic network of tangles, connect to one another randomly and criss-cross the stroma haphazardly [2-4, 11]. They are also strikingly heterogeneous and exhibit a spectrum of vesselsubtypes, ranging from capillaries and ‘mother’ vessels (big, leaky, thin-walled, pericyte-depleted fenestrated sinusoids) to glomeruloid vessel outgrowths and vascular malformations [4, 12]. Vessel diameters are uneven, because their wall is compressed by tumor or stromal cells, with some vessels being oversized, others being more immature smaller vessels, while in other areas, vessels are lacking altogether [13, 14]. Structural anomalies of the vessel wall, such as large gaps between endothelial cells, defects in pericyte coverage and function, discontinuous or absent basement membranes, and the pres - ence of pro-angiogenic molecules such as VEGF, contribute to the increased permeability of the tumor vessels [15]. The direct conse - quences are a slowing down of blood �ow veloc - Anti-angiogenesis or pro-angiogenesis for cancer therapy 8371 Int J Clin Exp Med 2015;8(6):8369-8376 ity and an increased out�ow of plasma macro - molecules (e.g., �brinogen), leading to a high oncotic pressure in the interstitium [10]. The complexity of this sc

enario is increased by the fact that vascular permeability varies spatially and temporally within the same tumor and between different tumors [15]. Furthermore, the capillary network is structurally abnormal and tortuous, with several loops and arteriove - nous shunts, and some vessels are com - pressed by the growing tumor cells. This causes an irregular blood �ow, changed hematocrit, and hemorrhages. Another aspect of heteroge - neity in intratumoral blood �ow is the so-called intermittent hypoxia [9]. It consists of reversible functional alterations in tumor blood vessels, and it seems to be caused by rapid �uctuations in hematocrit, temporary stagnation, local vas - cular remodeling, and alterations in vascular tone [9]. As a consequence, the delivery of not only blood-borne drugs but also oxygen and nutri - ents, as well as the clearance of products of metabolism, are reduced in some regions of the tumor tissue, which become hypoxic and acidic [16]. It is widely recognized that hypoxia and poor nutrition induce a more malignant phenotype of cancer cells through genetic and epigenetic mechanisms [17]. Therefore, the antineoplastic agents are not only physically limited in their access to the tumor bulk but are also compromised in their activity because cells in hypoxic, acidic, and nutrient-deprived regions engage resistance mechanisms [17]. Limitations of anti-angiogenesis therapy in cancer The seminal work by Folkman on tumor angio - genesis stimulated the discovery and develop - ment of many angiogenesis inhibitors [18]. The most validated anti-angiogenic strategies act on the VEGF axis, blocking VEGF directly with the neutralizing antibody bevacizumab or the a�ibercept (VEGF trap), or indirectly with low- molecular-weight tyrosine kinase VEGF recep - tor inhibitors (e.g., sunitinib, sorafenib, and pazopanib) [19]. Although promising results have been achieved preclinically and clinically, improvements to cur - rent anti-angiogenic therapies are still ongoing [20]. Some anti-angiogenic drugs have shown antitumor activity, mostly in combination with chemotherapeutics, but the mechanism of the increased ef�cacy when given in combination has not been fully elucidated. For example, some data suggest that anti-angiogenic thera - py can increase intratumoral hypoxia, leading to radioresistance and chemoresistance as well as potentially increasing metastasis, at least in mouse models [21, 22]. In terms of drug delivery, one would expect that the anti- angiogenic treatment, by altering tumor vascu - lature, impairs the delivery of chemotherapy. In fact, reducing angiogenesis did impair drug delivery to the tumor, ultimately restricting its ef�cacy [23]. The fact that the anti-angiogenic drugs enhance the response to anticancer drugs when given in combination suggests that they do not necessarily decrease drug delivery to tumor tissue. Jain [15] has proposed that anti-angiogenic drugs induce a process of vascular normalization. It is a transient rever - sion of the irregular tumor vasculature to a normal state, with a consequent drop in interstitial �uid pressure (IFP) and reduction of hypoxia, which provides an improvement of the penetration and activity of concurrent cytotoxic agents. Robust experimental evidence support - ing this theory is still lacking, and there are con�icting data in different preclinical models. In support of the normalization hypothesis, Wildiers et al. [24] showed that the administra - tion of an anti-VEGF monoclonal antibody to mice bearing a colon adenocarcinoma at 1 week before irinotecan administration causes a higher tumor perfusion and an increase in the intratumoral irinotecan concentration. Dickson et al. [25] reported that the treatment of ortho - topic neuroblastoma xenografts with bevaci - zumab results in a sustained decrease in both tumor vessel permeability and IFP, with a concomitant increase in intratumoral perfusion for 1 week. The penetration of topotecan and etoposide improved when given at 1-3 days after bevacizumab as compared with concomi - tant administration or with a dosing schedule with a 7-day interval [25]. These �ndings are consistent with the hypothesis that the effect of the anti-angiogenic therapy is transient, generating a narrow window of time during which synergy can be achieved. These effects seem to be limited not only temporally but also spatially: acting on a heterogeneous tissue, normalization probably occurs only in some regions of the tumor, where anti-angiogenic agents succeed in correcting the imbalance Int J Clin Exp Med 2015;8(6):8369-8376 www.ijcem.com /ISSN:1940-5901/IJCEM0008925 Review Article Anti-angiogenesis or pro-ang

iogenesis for cancer treatment: focus on drug distribution Dongsheng Huang 1 , Huanrong Lan 2 , Fanlong Liu 3 , Shibing Wang 1 , Xiaoyi Chen 1 , Ketao Jin 1,2 , Xiaozhou Mou 1 1 Clinical Research Institute, Zhejiang Provincial People’s Hospital, Hangzhou 310014, China; 2 Department of Gastrointestinal Surgery, Shaoxing People’s Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing 312000, Zhejiang Province, P.R. China; 3 Department of Surgical Oncology, The First Af�liated Hospital, Zhejiang University School of Medicine, Hangzhou 310003, Zhejiang, P.R. China Received April 9 , 2015; Accepted June 7 , 2015; Epub June 15, 2015; Published June 30, 2015 Abstract: Enhancing chemotherapy delivery to tumors, improving tumor growth control, reducing metastasis, and increasing survival are all critical objectives of improved cancer therapy. One of the obstacles to the success of anti - cancer therapies is related to the inef�cient distribution of drugs to tumor cells. To be effective, chemotherapeutics must reach a concentration in cancer cells that is suf�cient to inhibit its targets. In the past years, the vascular normalization theory has gained widespread acceptance for explaining additional antitumor effects of inhibitors of vascular endothelial growth factor (VEGF) signaling, when combined with chemotherapeutics. Vascular normal - ization is a strategy to enhance the antitumor effects of chemotherapeutics, but this is time and dose dependent and therefore dif�cult to implement clinically. Thus, alternative strategies that overcome these issues are needed. Accumulating scienti�c data demonstrate an alternative approach called “vascular promotion therapy” can increase chemotherapeutics delivery and intracellular uptake of the drug and reduces hypoxia by increasing tumor blood vessel density, blood �ow, leakiness, and dilation, which leads to reduced cancer growth and metastasis. In this article, we �rst summarize the structural and functional abnormalities of the tumor microvasculature to highlight the importance of this phenomenon for chemotherapeutics distribution. Next, we summarize the limitations of anti-angiogenic strategy in cancer treatment, discuss some key prototypical underlying mechanisms of vascular normalization and initial clinical evidence of vascular promotion therapy, and speculate on the clinical potential of anticoagulation as a novel paradigm to improve cancer treatment. Keywords: Antiangiogenesis, -proangiogenesis, anticoagulation, drug distribution Introduction Enhancing chemotherapy delivery to tumors, improving tumor growth control, reducing metastasis, and increasing survival are all criti - cal objectives of improved cancer therapy. One of the obstacles to the success of anticancer therapies is related to the inef�cient distribu - tion of drugs to cancer cells. To be effective, chemotherapeutics must reach a concentra - tion in cancer cells that is suf�cient to inhibit its targets. The causes of the inef�cient distribu - tion of the anticancer compounds in the tumor bulk are multiple and interconnected. Obviously, the penetration capacity of a drug depends on its physicochemical properties, but one of the key reasons for low delivery can be mainly ascribed to the tumor abnormal blood vessels, which constitutes a key obstacle to the homo - geneous distribution of chemotherapeutics to the tumor tissue. In the majority of cancers, vessel growth is not only stimulated, but these vessels are also abnormal in almost all aspects of their struc - ture and function [1-4]. This results in a hostile tumor microenvironment-characterized by hy- poxia, low pH and high interstitial hostile �uid pressure-that can alter the intrinsic characteris - tics of tumor cells such that malignant tumor clones are selected and escape of tumor cells through leaky vessels is facilitated [2]. Abnormal tumor vessels can also impede the function of immune cells in tumors, as well as the transport and/or distribution of chemotherapeutics and oxygen. As a result, the abnormal tumor vascu - Anti-angiogenesis or pro-angiogenesis for cancer therapy 8375 Int J Clin Exp Med 2015;8(6):8369-8376 [3] Baluk P, Hashizume H and McDonald DM. Cellular abnormalities of blood vessels as tar - gets in cancer. Curr Opin Genet Dev 2005; 15: 102-111. [4] Nagy JA, Chang SH, Shih SC, Dvorak AM and Dvorak HF. Heterogeneity of the tumor vascu - lature. Semin Thromb Hemost 2010; 36: 321- 331. [5] Teng LS, Jin KT, He KF, Wang HH, Cao J and Yu DC. Advances in combination of antiangiogen - ic agents targeting VEGF-binding and conven - tional chemotherapy and radiation for cancer treatment. J Chin Med Assoc 2010; 73: 281- 288. [

6] Batchelor TT, Sorensen AG, di Tomaso E, Zhang WT, Duda DG, Cohen KS, Kozak KR, Cahill DP, Chen PJ, Zhu M, Ancukiewicz M, Mrugala MM, Plotkin S, Drappatz J, Louis DN, Ivy P, Scadden DT, Benner T, Loef�er JS, Wen PY and Jain RK. AZD2171, a pan-VEGF receptor tyrosine kinase inhibitor, normalizes tumor vasculature and al - leviates edema in glioblastoma patients. Cancer Cell 2007; 11: 83-95. [7] Willett CG, Boucher Y, di Tomaso E, Duda DG, Munn LL, Tong RT, Chung DC, Sahani DV, Kalva SP, Kozin SV, Mino M, Cohen KS, Scadden DT, Hartford AC, Fischman AJ, Clark JW, Ryan DP, Zhu AX, Blaszkowsky LS, Chen HX, Shellito PC, Lauwers GY and Jain RK. Direct evidence that the VEGF-speci�c antibody bevacizumab has antivascular effects in human rectal cancer. Nat Med 2004; 10: 145-147. [8] Jain RK. Normalizing tumor vasculature with anti-angiogenic therapy: a new paradigm for combination therapy. Nat Med 2001; 7: 987- 989. [9] Bouzin C and Feron O. Targeting tumor stroma and exploiting mature tumor vasculature to im - prove anti-cancer drug delivery. Drug Resist Updat 2007; 10: 109-120. [10] Heldin CH, Rubin K, Pietras K and Ostman A. High interstitial �uid pressure - an obstacle in cancer therapy. Nat Rev Cancer 2004; 4: 806- 813. [11] Mazzone M, Dettori D, Leite de Oliveira R, Loges S, Schmidt T, Jonckx B, Tian YM, Lanahan AA, Pollard P, Ruiz de Almodovar C, De Smet F, Vinckier S, Aragones J, Debackere K, Luttun A, Wyns S, Jordan B, Pisacane A, Gallez B, Lampugnani MG, Dejana E, Simons M, Ratcliffe P, Maxwell P and Carmeliet P. Heterozygous de�ciency of PHD2 restores tu - mor oxygenation and inhibits metastasis via endothelial normalization. Cell 2009; 136: 839-851. [12] Pettersson A, Nagy JA, Brown LF, Sundberg C, Morgan E, Jungles S, Carter R, Krieger JE, Manseau EJ, Harvey VS, Eckelhoefer IA, Feng D, Dvorak AM, Mulligan RC and Dvorak HF. Heterogeneity of the angiogenic response in - duced in different normal adult tissues by vas - cular permeability factor/vascular endothelial growth factor. Lab Invest 2000; 80: 99-115. [13] Fukumura D, Duda DG, Munn LL and Jain RK. Tumor microvasculature and microenviron - ment: novel insights through intravital imaging in pre-clinical models. Microcirculation 2010; 17: 206-225. [14] Jain RK and Stylianopoulos T. Delivering nano - medicine to solid tumors. Nat Rev Clin Oncol 2010; 7: 653-664. [15] Jain RK. Normalizing tumor microenvironment to treat cancer: bench to bedside to biomark - ers. J Clin Oncol 2013; 31: 2205-2218. [16] Tredan O, Galmarini CM, Patel K and Tannock IF. Drug resistance and the solid tumor micro - environment. J Natl Cancer Inst 2007; 99: 1441-1454. [17] Minchinton AI and Tannock IF. Drug penetra - tion in solid tumours. Nat Rev Cancer 2006; 6: 583-592. [18] Folkman J. Angiogenesis: an organizing princi - ple for drug discovery? Nat Rev Drug Discov 2007; 6: 273-286. [19] Cesca M, Bizzaro F, Zucchetti M and Giavazzi R. Tumor delivery of chemotherapy combined with inhibitors of angiogenesis and vascular targeting agents. Front Oncol 2013; 3: 259. [20] Shojaei F. Anti-angiogenesis therapy in cancer: current challenges and future perspectives. Cancer Lett 2012; 320: 130-137. [21] Ebos JM, Lee CR, Cruz-Munoz W, Bjarnason GA, Christensen JG and Kerbel RS. Accelerated metastasis after short-term treatment with a potent inhibitor of tumor angiogenesis. Cancer Cell 2009; 15: 232-239. [22] Paez-Ribes M, Allen E, Hudock J, Takeda T, Okuyama H, Vinals F, Inoue M, Bergers G, Hanahan D and Casanovas O. Antiangiogenic therapy elicits malignant progression of tu - mors to increased local invasion and distant metastasis. Cancer Cell 2009; 15: 220-231. [23] Van der Veldt AA, Lubberink M, Bahce I, Walraven M, de Boer MP, Greuter HN, Hendrikse NH, Eriksson J, Windhorst AD, Postmus PE, Verheul HM, Serne EH, Lammertsma AA and Smit EF. Rapid decrease in delivery of chemotherapy to tumors after anti-VEGF therapy: implications for scheduling of anti-angiogenic drugs. Cancer Cell 2012; 21: 82-91. [24] Wildiers H, Guetens G, De Boeck G, Verbeken E, Landuyt B, Landuyt W, de Bruijn EA and van Oosterom AT. Effect of antivascular endothelial growth factor treatment on the intratumoral uptake of CPT-11. Br J Cancer 2003; 88: 1979- 1986. Anti-angiogenesis or pro-angiogenesis for cancer therapy 8374 Int J Clin Exp Med 2015;8(6):8369-8376 ef�cacy when given in combination with che - motherapy. Improving the hypercoagulable or prothrombotic state of malignancy to reinforce the antitumor ef�cacy of vascular normaliza - tion or vascular promotion therapy in combina - tion with chemotherapy is highly desirable. With these issues in mind, researchers began to explore the potential application of antico - agulation as adjuvant therapy for t

reatment of cancer. Aspirin, for example, several important observational studies published in the past 3 years strongly indicate that aspirin treatment after (or before) the diagnosis of colorectal cancer reduces distant metastasis and improves colorectal cancer-speci�c mortality [43, 44]. Herein, we hypothesize that anticoagulation therapy in combination with vascular normal - ization of anti-angiogenic agents or vascular promotion therapy and chemotherapeutics could result in a synergic antitumor ef�cacy. This hypothesis based on the following facts: Firstly, anticoagulation therapy can improve the hypercoagulable state of tumors, increase the penetration capacity of chemotherapeutics, and improve the ef�cient distribution of chemo - therapeutics to cancer cells, which result in enhanced antitumor ef�cacy of chemotherapy. Furthermore, anticoagulation therapy can improve the microvascular environment to decrease the appearance of deep vein throm - bosis and decrease the mortality and morbidity in cancer patients. Secondly, vascular normal - ization of anti-angiogenic agents can enhance the delivery and antitumor activity of chemo - therapy by remodeling tumor vessels to a struc - tural and functional phenotype more re�ective of normal blood vessels and overcoming the physiological barriers to drug delivery within tumors through improvement in their functional ef�ciency. Thirdly, vascular promotion therapy can increase chemotherapy delivery and intra - cellular uptake of the drug by increasing tumor blood vessel density, blood �ow, leakiness, and dilation. Conclusion Vascular normalization of VEGF inhibitors is a strategy to enhance the antitumor effects of chemotherapeutics, but this is time and dose dependent and therefore dif�cult to implement clinically. Vascular promotion therapy and anti - coagulation therapy are now emerging as novel opportunities to improve the ef�cacy of anticancer therapy. A greater awareness of the concept of vascular promotion and anti - coagulation in human cancer will further stimu - late interest in studying these processes. Though the therapeutic bene�ts of vascular promotion and anticoagulation in human can - cer remain only indirectly proven to date, emerging preclinical evidence would increas - ingly support the paradigm that vascular pro - motion and anticoagulation strategies can be bene�cial. None-theless, many challenges remain to be add-ressed in order to fully exploit the therapeutic potential of vascular promotion and anticoagulation in cancer patients. Acknowledgements This work was supported by National Natural Science Foundation of China (Grants No. 81374014, No. 81201783, No. 81372463 and No. 81472210), Zhejiang Provincial Med- ical and Healthy Science and Technology Projects (Grant No. 2013KYA228), Zhejiang Provincial Science and Technology Project (Grant No. 2013C33112), the Traditional Chinese Medicine Scienti�c Research Found- ation of Zhejiang Province (2015ZA009), Science Research Fund of Taizhou (Grants No. A121KY08, A131KY13-3 and A131KY13-12), and Enze Medical Research Fund (Grants No. 12EZA1, 13EZA2 and 13EZB6). Disclosure of con�ict of interest None. Address correspondence to: Dr. Ketao Jin, Department of Gastrointestinal Surgery, Shaoxing People’s Hospital, Shaoxing Hospital of Zhejiang University, No. 568, Zhongxing North Road, Shaoxing 312000, Zhejiang Province, P.R. China. E-mail: jin - ketao2001@zju.edu.cn; Dr. Xiaozhou Mou, Clinical Research Institute, Zhejiang Provincial People’s Hospital, No. 158 Shangtang Road, Hangzhou 310014, Zhejiang Province, P.R. China. E-mail: mouxiaozhou@gmail.com References [1] Shi S, Chen L and Huang G. Antiangiogenic therapy improves the antitumor effect of adop - tive cell immunotherapy by normalizing tumor vasculature. Med Oncol 2013; 30: 698. [2] Jain RK. Normalization of tumor vasculature: an emerging concept in antiangiogenic thera - py. Science 2005; 307: 58-62. Anti-angiogenesis or pro-angiogenesis for cancer therapy 8373 Int J Clin Exp Med 2015;8(6):8369-8376 in vivo were higher when administered in com - bination with cilengitide and verapamil. The authors then investigated whether this increase in blood vessel density, dilation, perfusion and permeability resulted in increased delivery of gemcitabine. Gemcitabine uptake into cells is regulated by equilibrative nucleoside transport - er 1 (ENT1) and ENT2, as well as by concentra - tive nucleoside transporter 3 (CNT3), which mediates the unidirectional �ow of the drug into the cell. Once inside the cell, gemcitabine is metabolized by deoxycytidine kinase (DCK). In vitro experiments sho

wed that treatment with the triple combination increased the expression levels of ENT1 and ENT2, as well as the expression of CNT3, which increased the in�ux of gemcitabine. Low doses of cilengitide also increased DCK expression, thus increas - ing the overall ef�cacy and potency of gem - citabine. This study provided an interesting approach to cancer treatment by promoting, rather than inhibiting, vascular formation. These results are unexpected and call for con - sideration of vascular promotion strategies in combination with chemotherapy for the treat - ment of cancer. These results point toward a possible radical change in therapeutic strategy by vascular promotion which allows signi�cant - ly reduced doses of chemotherapeutics to be used effectively. By enhancing intratumoral delivery and intracellular uptake of the cytotox - ic drug, vascular promotion therapy can mini - mize adverse effects of the therapy, while enhancing its ef�cacy. Thus, this strategy could provide the opportunity to extend treatment duration without reducing quality of life. Anticoagulation in cancer treatment: perspec - tives A hypercoagulable or prothrombotic state of malignancy occurs due to the ability of tumor cells to activate the coagulation system. It has been estimated that hypercoagulation accou- nts for a signi�cant percentage of mortality and morbidity in cancer patients. There is consider - able evidence that thrombosis is a common complication of malignancy, and represents the second most frequent cause of death in cancer patients [34, 35]. A broad spectrum of clinically signi�cant hemostatic abnormalities may af�ict as many as 15-25% of cancer patients. Furthermore, hemostatic complications are the second most common cause of mortality in cancer patients, particularly in those with pan - creatic, gastrointestinal or lung cancer, and 10% of newly diagnosed myeloma patients treated with any type of chemotherapy develop deep venous thrombosis [35-37]. Anticancer therapy (i.e., surgery/chemotherapy/hormone therapy) may signi�cantly increase the risk of thromboembolic events by the mechanisms, such as procoagulant release, endothelial damage, or stimulation of tissue factor produc - tion by host cells [35]. Chemotherapy can increase the risk of thrombosis in cancer patients. This has been best studied in breast cancer, where tamoxifen and cytotoxic chemo - therapy both appear independently to increase the risk of venous thrombosis [35]. Acute arte - rial thrombotic events were also reported to be induced by cytotoxic chemotherapy especially in patients receiving platinum-based chemo - therapy [38, 39]. The impact of cancer cells and chemotherapy on the activation of the coagulation cascade is responsible for a pro- thrombotic state found in many cancer patients [40]. Various mechanisms related to the activa - tion of the coagulation or �brinolytic systems in cancer may be involved in tumor development, progression and metastasis. Activation of coagulation can have both systemic and local consequences. The systemic consequences involve deep vein thrombosis or metastasis. Local consequences involve the deposition of �brin and plasma proteins in the tumor inter- stitium, resulting at least in part, from tumor vasculature that is inherently leaky. This �brin deposition results in imposition of the initial tumor structure, regulation of in�ammatory cell in�ltration, induction of angiogenesis and formation of a mature stroma. In addition, accumulation of �brin and other plasma proteins in the tumor microenvironment con - tributes signi�cantly to increased interstitial pressure that impedes the penetration of chemotherapeutic agents into the tumor [8, 41, 42]. Tumor generated polymerized �brin also results in the formation of a physical barrier protecting the tumor from natural killer cells and other exogenous anticancer agents. Although vascular normalization of anti-angio - genic agents can transiently remodel tumor vessels and partially overcome the physiologi - cal barriers to drug and oxygen delivery within tumors and vascular promotion therapy can increase chemotherapy delivery and intracellu - lar uptake of the drug, these strategies cannot reverse the hypercoagulable or prothrombotic state of malignancy and restrict their synergic Anti-angiogenesis or pro-angiogenesis for cancer therapy 8372 Int J Clin Exp Med 2015;8(6):8369-8376 between pro- and anti-angiogenic factors. Consequently, it is of the utmost importance to carefully de�ne the timing of the normalization window, the scheduling, and the dosing of anti- angiogeni

c therapies in order to optimize the ef�cacy of a combination of antitumor strate - gies. Pastuskovas et al. [26] reported that in human epidermal growth factor receptor-2 (HER-2) expressing breast cancer xenografts, bevacizumab causes reduced tumor uptake of trastuzumab, a monoclonal antibody directed against HER-2, probably because of the blood �ow and vascular permeability reduction. Cesca et al. [27] and Bello et al. [28] investi - gated the tumor concentrations of paclitaxel given in combination with small-molecular tyrosine kinase inhibitors with an anti-angio - genic effect in xenograft models. It was found that the tumor concentration of paclitaxel decreases when the anti-angiogenic compound is administered before paclitaxel. Nevertheless, the combined treatment improved antitumor activity. Chauhan et al. [29] reported that in murine models of breast cancer, blocking VEGF receptor 2 with an antibody increases the deliv - ery of nanoparticles of 12 nm diameter while it hampers the delivery of larger nanoparticles (125 nm diameter). They suggested that the anti-VEGF treatment causes a reduction in size of the holes in tumor vasculature, thus produc - ing discrepant effects on extravasation of mol - ecules depending on their size. The available clinical information on the in�uence of anti- angiogenic drugs on the distribution of antican - cer drugs given in combination is limited. Willet et al. [7] performed a study in six patients with rectal adenocarcinoma showing that bevaci - zumab at the dose of 5 mg/kg in combination with 5-�uorouracil and radiotherapy is able to reduce the IFP from 15 to 4 mmHg. This effect was associated with decreased tumor blood perfusion and vessel density. Unfortunately, no data on the tumor concentration of 5-�uoroura - cil were reported. In another clinical setting, Van der Veldt et al. [23] obtained discrepant results. In 10 non-small cell lung cancer patients, the administration of bevacizumab (15 mg/kg, infused over 90 min) reduced both perfusion and net in�ux rate of [11C] docetaxel as visualized by positron emission tomography (PET). The effect lasted from 5 h to 4 days after infusion of bevacizumab. Supporters of the nor - malization theory claim that this treatment schedule constitutes excessive or unduly pro - longed dosing of bevacizumab, which can lead to rapid vascular regression or to the activation of alternative pro-angiogenic pathways, thus hampering docetaxel delivery. This counter-pro - ductive effect could also be responsible for the lack of ef�cacy of bevacizumab given in combi - nation in phase III breast cancer trials. Pro-angiogenesis in cancer treatment Vascular normalization, using anti-angiogenic agents, is the process by which partial loss of blood vessel density is associated with a tem - porary increase in blood �ow [30]. This approach has shown signi�cant promise [6, 31], but since it relies on a temporal window of opportunity that is both time and dose depen - dent and may well be different for different cancer types, it is generally considered dif�cult to implement clinically [32]. Thus, the para - digms that underlie anti-angiogenic and vascu - lar normalization strategies are still open for improvement. Designing vascular modulation strategies that overcome at least some of these issues is highly desirable. With these issues in mind, Wong et al. [33] have proposed an alternative approach called “vascular promotion therapy”. Low doses of the anti-angiogenic drug cilengitide can enhance tumor angiogenesis, and the calcium channel blocker verapamil can increase vessel dilation and blood �ow; therefore, the authors hypothe - sized that these two agents would improve delivery of the chemotherapeutic agent gem - citabine when administered in combination. To that end, they assessed the ability of these agents to inhibit tumor growth and metastasis in a xenograft mouse model of lung cancer and in a mouse model of spontaneous pancreatic cancer. Whereas treatment with gemcitabine alone had no apparent effect compared with placebo, treatment with the triple combination of cilengitide-verpamil-gemcitabine reduced tumor burden and number of metastases con - siderably, and these effects were sustained after cessation of treatment. Analysis of the tumor vasculature showed that the triple com - bination increased blood vessel density and perfusion compared with treatment with gem - citabine alone. Further experiments demon - strated that the combination treatment increased vessel leakage and reduced tumor hypoxia, therefore suggesting a potential enhanced intratumoral drug delivery. Indeed, gemcitabine concentrations in the whole